PB1780: DIFFERENCES IN SECRETOME OF BONE MARROW MULTIPOTENT MESENCHYMAL STROMAL CELLS IN PATIENTS AT THE ONSET OF ACUTE MYELOID LEUKEMIA AND AFTER ACHIEVING REMISSION.
Authors: Aleksandra Sadovskaya, Nataliya Petinati, Nina Drize, Igor Smirnov, Olga Pobeguts, Georgiy Arapidi, Maria Lagarkova, Anastsia Vasilieva, Olga Gavrilina, Elena Parovichnikova
Journal: HemaSphere (2023)

Topic: 3. Acute myeloid leukemia - Biology & Translational Research Background: Multipotent mesenchymal stromal cells (MSCs), their descendants and the proteins secreted by them, are essential hematopoiesis regulators. In patients with acute myeloid leukemia (AML) malignant cells change MSCs’ properties and reduce their ability to maintain normal hematopoiesis. A detailed study of MSCs secretome at the onset of the disease and in remission may elucidate the role of MSCs in supporting cancer cells and restoration of normal hematopoiesis. Aims: The aim of this work was to study general changes in secretome of MSCs in patients with AML at the onset of the disease and in remission. Methods: The study included MSCs obtained from the bone marrow of 13 AML patients: (3 male, 10 female, median age 38) and 21 donors (10 male, 11 female, median age 35) that were used as control. All donors and patients signed informed consent. MSCs were cultured by standard method. The analysis of proteins contained in the MSCs-conditioned medium was performed on an Orbitrap Q Exactive HF-X mass spectrometer equipped with a nano-electrospray source and a high-pressure nanoflow chromatograph (UPLC Ultimate 3000) with a C-18 (100um) reverse-phase column x 300mm. The results were analyzed in Scaffold 5 (version 5.1.0) for validation and meta-analysis. For functional enrichment analysis we selected the proteins that had ǀlogFCǀ>2 and the differences in secretion of which were significant (p<0.05). Results: A total of 2833 proteins were identified, of which 582 were differentially secreted by patients’ and donors’ MSCs (Figure). Some proteins, including those involved in proteolysis, cellular protein metabolic process and regulation of hydrolase activity, were secreted by MSCs of patients at AML onset, but not in donors’. MSCs from primary patients secreted higher levels of proteins related to immune regulation, cell adhesion, and extracellular matrix organization. MSCs of patients at the onset of AML secreted lower levels of proteins responsible for platelet activity, aging, differentiation, and angiogenesis. Protein secretion by patients’ MSCs differs little between onset of AML and remission. Proteins belonging to the extracellular matrix organization were reduced in remission compared to the onset of the disease. Upon reaching remission secretion of proteins related to lysosomes and exosomes increased. The most pronounced differences between the MSCs’ secretome composition at the onset and that in remission were revealed in comparison with donors. The most differences of donors’ and AML MSCs’ secretome were the same for onset and remission. The unique differences between AML onset and donors were decreased levels of proteins related to ossification, transport and immune response. In remission, but not at the onset, proteins responsible for cell adhesion, immune response, complement and coagulation cascades were reduced compared to donors. Extracellular matrix organization and vesicular transport were disorganized: every comparison revealed alterations in different proteins related to these processes. Summary/Conclusion: AML causes crucial changes in the MSCs’ secretome. Some secretome modifications caused by the tumor are reversed upon achieving remission, but not all of them. Chemotherapy leads to new alterations. Thus, in remission, in the absence of tumor cells and with the formation of normal hematopoietic cells, the functions of MSCs remain impaired. The study was supported by a grant from the Russian Science Foundation project № 22-15-00018, https://rscf.ru/project/22-15-00018/Figure. Diferentially secreted proteins Keywords: Secretion, Acute myeloid leukemia, Mesenchymal stem cell